Gas resupply valve with microscopic aperture for gas lasers

ABSTRACT

There is disclosed herein several gas resupply valves for replenishment of lost gas in gas lasers in general and argon ion lasers in particular. The first embodiment uses a valve which controls flow of gas into a metering volume. The metering volume has an aperture therein which is microscopically small and which has a diffusion constant for gas moving through the aperture which is less than the time the valve is held open. The second embodiment uses the same general structure, but separates the soft sealing member of the valve from the solenoid core which moves to open and close the valve. The soft sealing member is attached to the valve body and supported above a valve seat surrounding the opening of the metering volume. The third embodiment uses a thin diaphragm which overlies a flat surface of the valve body in which are formed an input port and an output port. A solenoid applies pressure against the diaphragm to cause it to flatten against the flat surface thereby sealing the valve.

BACKGROUND OF THE INVENTION

The invention relates generally to the field of gas lasers which have loss mechanisms and, more particularly, to the field of gas resupply valves for such gas lasers to supply new gas to maintain gas pressure within the laser tube within acceptable limits.

In almost all gas lasers there is a loss mechanism whereby gas molecules trapped in the laser tube are lost either through leaks or through chemical combination with or sputtering into the materials on the inside of the laser tube. In the field of ion lasers, and especially in the field of argon ion lasers, the argon atoms are ionized by electrical discharges passing through the gas-filled laser tube. These ions are then excited to higher energy states by pumping energy supplied from an outside source. Although argon is a noble gas, argon ions can "sputter" into the walls of the laser tube and be lost for further laser action. Because there is a very narrow band of acceptable pressures for gas in the laser tube which will cause lasing action, it is important that the pressure of argon gas in the laser tube remain relatively constant. Thus, when argon ions are lost, pressure in the laser tube will drop. This loss of pressure can be detected by monitoring the voltage appearing across the electrodes which ionize the argon gas since the voltage drops as the pressure drops. If the lost argon ions are not replaced with new gas molecules, the laser will become unstable. If the pressure in the gas tube drops low enough, the laser will stop lasing.

In the prior art, the lost gas has been replaced by the use of gas resupply valves. These valves have small reservoirs for storing argon gas at atmospheric pressure (or any other pressure) and have metering volumes. When the pressure in the laser gets too low, the metering volume is filled with gas through a valve and this gas is then allowed to enter the highly evacuated laser tube to replenish the gas supply. The use of the metering volume allows a known quantity of gas to be injected into the laser tube on each "charging" cycle. Very tiny amounts of gas are involved in this process. This is because if too much gas is allowed to enter the laser tube, the laser can be essentially ruined since higher pressures mean higher voltages between the ionization electrodes which the power supplies are not designed to handle. When too much gas enters the tube, the tube must be sent back to a refurbishing facility for reprocessing to get the pressure back down to an acceptable level.

The requirements for a gas resupply valve for gas lasers are three. First, the valve must have a negligible leak rate when the valve is closed. This is required so that gas laser tubes which sit in inventory unused for many weeks or months do not leak gas to the extent that the laser becomes unusable or inoperative before it is ever used. A second requirement is that the valve have a lifetime of at least 1,000 cycles between open and closed positions without failure or degradation in the residual leak rate when the valve is closed. Finally, such gas resupply valves must have extremely short cycle times between opening and closing in embodiments where only one valve member and a controlled leak aperture is used. There are prior art embodiments to be discussed below which use two valve members. For these valves, it is not necessary that the cycle time be as small as noted above. But all gas resupply valves must meet the first two requirements.

An early gas resupply valve design known to workers in the art used two valve seats and two valve members. The metering volume was the volume trapped between the valve seats when the two valve members were seated on their respective valve seats. A chamber around one valve was coupled to the gas reservoir, and the other valve opened into the gas laser tube or another tube coupled thereto. In operation, the "reservoir" valve was opened for a time sufficient to cause the metering volume to fill up with replacement gas at the pressure of the reservoir. After the metering volume was full, the "reservoir" valve was closed and the second or "laser tube" valve was opened thereby allowing the gas in the metering volume to be drawn into the laser tube, which has an internal pressure much lower than atmospheric pressure, to replenish the supply of gas therein.

The difficulty with this design was that two valves and corresponding driving mechanisms were necessary. This made the valve relatively expensive, and more parts were present to fail.

In an effort to simplify this design, workers in the art eliminated one of the valves and replaced it with a capillary tube having an inside diameter of five thousandths of an inch. This capillary tube had a diffusion constant which was longer than the interval during which the first valve coupled to the reservoir was opened. The capillary tube was connected to the interior of the laser gas tube. In operation, the first valve coupled to the reservoir was opened for a very short time which was shorter than the diffusion constant of the capillary tube. During this time the replacement gas from the reservoir filled the metering volume. The diffusion constant of the capillary tube had to be long compared to the time of opening of the first valve so that the capillary tube not appear as a leak. When this was true, the metering volume appeared to have no leak therein during the time that the valve was open, and the amount of gas that entered the metering volume could be accurately predicted. After the valve was closed and the diffusion time constant had passed, the gas trapped in the metering volume leaked into the laser tube through the capillary tube to replenish the laser tube gas supply.

One difficulty with this approach was that the capillary tube was difficult to keep clean. In order to have a diffusion constant which was smaller than the open time of the valve, it was necessary to use a capillary tube with a very small inside diameter. This made it extremely difficult to keep the bore of the capillary tube clean and resulted in contaminants in the capillary tube being sucked into the laser tube. The resultant contamination caused failure of laser tubes. Another difficulty with the capillary tube design was that the capillary tube acted as a virtual leak in the laser tube during the evacuation step of the process of manufacturing the laser tube. During manufacture of a gas laser, the tube is pumped down to the desired vacuum level prior to filling it with the desired gas. The virtual leak represented by the capillary caused the time to pump the laser tube down to the necessary level to be longer than would otherwise be necessary. Those skilled in the art will appreciate that the capillary tube coupled to the metering volume appears to be a crevice in the wall of the tube which couples into a cavern. In order for the laser to be effectively evacuated, all the gas molecules in the metering volume and the capillary tube had to be pumped out through the restrictive passageway presented by the capillary tube.

Thus a need exists for a simple, reliable, relatively inexpensive gas resupply valve for gas lasers.

SUMMARY OF THE INVENTION

According to the teachings of the invention, a gas resupply valve is taught using a metering volume which uses one valve at an inlet and which has an outlet comprised of one wall which has a microscopically small aperture therein. Typically, this aperture is laser drilled and has a diameter of from 10-15 microns. The valve opens for a predetermined interval to gate gas from the gas reservoir into the metering volume. Input gas comes from a resupply gas reservoir coupled to a chamber surrounding the valve. The small aperture in the wall of the metering volume is in fluid communication with the interior of a gas laser tube such that the vacuum level in the gas laser tube is present in the metering volume at all times except when the valve is open. The gas resupply reservoir is at atmospheric pressure typically however any pressure could be used. When the valve opens, the lower pressure in the metering volume causes gas from the reservoir and the chamber surrounding the valve to enter the metering volume. However, the aperture size and length is such that the diffusion constant for gas molecules moving through this aperture into the laser tube is longer than the time during which the valve is open. Thus, the metering volume is a virtual closed cavity as long as the valve is not open for a time which is longer than the diffusion constant for the aperture.

The wall of the metering volume having the aperture therein is thin so that the length of the aperture is short. Thus the aperture has a length which is short compared to the 1 to 2 inches of capillary tube used in prior art valves. This makes the aperture far easier to clean than the prior art capillary tubes. Conventional laser drilling techniques may be used to form the aperture. Any conventional technique such as chemical machining may be used to make the aperture. The critical element is that the size and length of the aperture cause it to have a diffusion constant which is longer than the time during which the valve will be open on each "charging cycle".

After the valve is closed, the gas in the metering volume leaks into the interior of the laser tube through the aperture. The voltage across the laser tube is then monitored during operation to determine if the amount of gas metered into the laser tube is sufficient to bring the pressure back to within the desired pressure range. If the gas charge is insufficient, one or more additional gas charges is provided by cycling the valve open and closed one or more times. This process is repeated until the pressure rises to the desired pressure range and the voltage across the tube rises to the desired level.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a gas resupply valve according to the teachings of the invention.

FIG. 2 is a cross sectional view of a gas resupply valve according to another embodiment of the invention.

FIG. 3 is a cross sectional view of a gas resupply valve according to the preferred embodiment of the invention.

FIG. 4 is a cross sectional view of a gas resupply valve having a flat metal diaphragm according to another embodiment of the invention.

FIG. 5 is a cross sectional view of a valve having a flat metal diaphragm according to another embodiment of the invention useful outside the field of gas lasers.

FIG. 6 is a cross sectional view of a valve having a flat metal diaphragm which attached to the valve body at welds and which has folds in the diaphragm to relieve stresses of any origin which might cause the diaphragm to bow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a cross-section of a gas laser resupply valve having one valve and a small aperture in a wall of the metering volume. The valve is comprised of a resupply reservoir 10 which is filled with, for example, argon gas at atmospheric pressure. In the preferred embodiment, this resupply reservoir 10 can be a chamber machined in the body 12 of the valve. In other embodiments, the reservoir 10 may be coupled to the body of the valve through an external port (not shown).

The resupply reservoir 10 is coupled via a fluid passageway 14 to a chamber 16 containing a valve 18. This valve is comprised of a solenoid slug 20 and a softer material 22 on the end of the solenoid slug. The softer material must be capable of cold flow so that a seal may be formed but must be tough enough to withstand at least 1000 cycles of the valve. In the preferred embodiment, this softer material 22, which will hereafter be called the sealing member, is a polymer marketed by DuPont under the trademark CALRES.

The solenoid slug 20 is driven linearly along the y axis to open and close the valve to allow gas from chamber 16 to enter a metering volume 24. One wall of the metering volume 24 is comprised of a diaphragm 25. This diaphragm has formed therein by any known process a very small aperture 28. In the preferred embodiment, this aperture has a diameter of from 10-15 microns and is laser drilled. The thickness of the diaphragm 25 is not critical other than it must be such as to establish the diffusion time of gas moving through the length of the aperture 28 along the negative y axis. Also, the diaphragm 25 must have sufficient thickness to withstand pressures exerted on it during the short time when the metering volume has been filled with gas at atmospheric pressure and gas is leaking through the aperture 28 into the laser tube.

The valve opens when the CALRES™ sealing member 22 leaves contact with a valve seat 26. The valve closes when the sealing member 22 again is reestablished in contact with the valve seat 26 under the influence of the solenoid slug 20. In the preferred embodiment, the solenoid slug 20 moves in the direction of the positive y axis to open the valve. Typical open times are on the order of 5 milliseconds.

The valve 18 may have a different construction in other embodiments. Further, other open times may be used for the valve 18. It is critical, however, that the open time selected be less than the diffusion time for gas moving through the aperture 28.

The gas in chamber 16 is sealed therein by a sealing member 32 which is sealed to the body 12 by a copper washer 34 and sealing ribs 36 and 38.

In operation, the valve 18 opens thereby creating a path between the sealing member 22 and the valve seat 26 through which gas from chamber 16 flows into the metering volume. The solenoid slug 20 then moves in the negative y direction thereby forcing the sealing member 22 to make sealing contact with the valve seat 26. Because the laser tube coupled to fluid communication path 30 is at low pressure, and because the gas in chamber 16 is at atmospheric pressure, gas from chamber 16 naturally flows into metering volume 24. However, the diffusion time constant of gas moving through the aperture 28 is long compared to the time during which sealing member 22 is not in contact with valve seat 26. Thus, virtually no gas escapes from the metering volume 24 into the fluid communication path 30 and the corresponding laser tube during the time the valve is open. This is important so that precise control over the amount of gas which is injected into the laser tube is maintained. If too much gas is injected, the laser tube will reach too high a pressure and be out of the optimum range for lasing action. In such a situation, there is no way to get gas out of the tube in the field, and the laser may be out of service. After the sealing member 22 has sealed the metering volume 24, the diffusion time passes and the gas trapped in the metering volume 24 escapes through the aperture 28 into the lower pressure laser tube via fluid communication path 30. This process may be repeated as many times as necessary to raise the pressure in the laser tube to within the desired pressure range and to raise the voltage across the laser tube to the desired voltage.

Referring to FIG. 2, there is shown a cross-sectional view of another gas resupply valve according to the teachings of the invention. The valve is comprises a valve body 40 which has a valve seat 42 and a metering volume 42 formed therein. The metering volume has one wall which is a diaphragm 46. This diaphragm has an aperture 48 formed therein generally by laser drilling or any other convention process that can make an aperture from 10 to 15 microns in diameter. The size of the aperture 48 is determined by the same considerations used to determine the size of the aperture 28 in FIG. 1. The aperture 48 couples the metering volume 44 to a fluid communication pathway 50. This fluid path couples the metering volume 44 to the internal volume of the laser tube.

A valve is formed by the interaction between a sealing member 52 and the valve seat 42 under the influence of forces generated by a solenoid slug 54 and a spring 56. The sealing member 52 is a flexible material capable of cold flow such as CALRES™ by DuPont. The spring 56 engages an annular shoulder 58 formed on the solenoid slug 54 and forces the slug 54 in the negative y direction. This causes the sealing member 52 to deform to the position shown in dashed lines at 60. In this position, the underside of the sealing member 52 engages the valve seat 42 with sufficient force to cause the valve seat to cause slight indentations in the sealing member 52 by cold flow. This establishes a seal. When the valve is to be opened, a solenoid coil (not shown) driven by a pulse of approximately 5 milliseconds duration causes the solenoid slug 54 to move in the positive y direction sufficiently to allow the sealing member 52 to disengage the valve seat 42. This movement to disengage the valve seat happens without any external force being applied to the sealing member 52 by virtue of the elastic properties of the sealing member. That is, the sealing member 52 must have sufficient elasticity and memory to spring back to its undeformed position from the position 60 when force by the solenoid slug is released.

Note that in FIG. 2 the sealing member 52 is not physically attached to the solenoid slug 54 whereas in the valve shown in FIG. 1, the sealing member 22 is physically attached to the solenoid slug 20. Thus, if the solenoid slug 20 wobbles or rotates during its movement in the valve of FIG. 1, the sealing member 22 will not always engage the valve seat 26 in the same relative positions on the surface of the sealing member. If this happens, the resealing of the sealing member 22 to the valve seat 26 takes somewhat longer than if the sealing member 22 always strikes the valve seat 26 at the same place.

In the valve shown in FIG. 2, the sealing member 52 is supported by a spacer ring 62 and the valve body as opposed to being supported by the solenoid slug. This means that the sealing member remains stationary even if the solenoid slug 54 wobbles, rotates or otherwise moves during its travel along the y axis. The instability of the solenoid slug results quite frequently since a very loose fit between the solenoid slug and its support is necessary to keep friction acting on the slug down. This is necessary because of the very small opening time of the slug, i.e., on the order of 5 milliseconds. If too much friction is present, the cycle time to open and close the valve will be longer than the diffusion time constant. This means that the sealing member 52, when deformed to the position 60, always has the valve seat 42 strike the undersurface of the sealing member at the same location. This results in the cold flow indentations in the sealing member 52 being engaged with the tips of the valve seat 42 as a perfect match. That is, the cold flow indentations in the undersurface of the sealing member 52 will be perfectly matched in shape to the tips of the valve seat 42. The perfect match results because the tips of the valve seat cause the cold flow indentations in the first place. Because the sealing member 52 always maintains its position relative to the tips of the valve seat 42, the valve seat never has to form new indentations in the undersurface of the sealing member 52. This improves the resealing time from approximately 20 milliseconds for the valve shown in FIG. 1 to approximately 1 millisecond for the valve shown in FIG. 2. The resealing time is the interval between the time when the sealing member 52 first contacts the valve seat 42 to the time when gas flow into the metering volume 44 ceases.

The spacer ring 62 is engaged in a well 64 formed in the valve body 40 and serves to hold the sealing member 52 above the valve seat 42 in the positive y direction by a small distance. This distance is shown as dimension A in FIG. 2. It should be not so great that the sealing member 52 is incapable of deforming far enough to engage the valve seat 42. But the distance should be large enough to allow the metering volume 44 to fill rapidly during the 5 milliseconds or so that the sealing member 52 is not engaged with the valve seat 42 during a charging cycle.

The valve body 40 also has formed therein a gas reservoir 66 which is coupled to the well 64 by a gas passageway 68. The gas reservoir 66 stores a volume of gas which is identical to the gas in the laser tube. This gas is stored at atmospheric pressure generally.

The valve body 40 has sealing teeth 70 and 72 (actually this is one annular tooth) which engage a copper sealing washer 74. The surface of the sealing washer 74 having the most positive y coordinate is engaged by sealing teeth of 76 and 78 of a cap member (not shown) which forms a gas tight chamber surrounding the metering volume 44, the sealing member 52 and the solenoid slug 54. Thus, if any gas in well 64 gets past the sealing member 52 to the vicinity around the solenoid 54, that gas is trapped in the structure.

In operation, when a recharge cycle is to be performed, a short pulse, generally 5 milliseconds in duration, is applied to the solenoid coil which drives the solenoid slug 54 in the positive y direction. This disengages the sealing member 52 from the valve seat 42 thereby allowing gas at atmospheric pressure in well 64 to fill the metering volume 44. No gas escapes through the aperture 48 into the fluid passageway 50 since the diffusion time constant for gas moving through the aperture 48 is longer than the time which the valve is open. After the pulse to the solenoid coil returns to zero voltage, the spring 56 exerts a force on the annular shoulder 58 sufficient to cause the solenoid slug 54 to move in the negative y direction. This causes a force on the sealing member 52 which causes it to deform to the position 60. This closes the valve and cuts off fluid communication with the well 64. A known amount of gas is then trapped in the metering volume since the volume of this chamber is known and it is known that no gas could have escaped through the aperture during the 5 millisecond fill time. Gas trapped in the metering volume 44 then leaks through the aperture 48 into the lower pressure laser tube via passageway 50. This process is repeated as many times as necessary to raise the pressure in the laser tube to within the desired pressure range.

Referring to FIG. 3, there is shown another embodiment of the valve of FIG. 2. The main difference between the embodiment shown in FIG. 3 and the embodiment shown in FIG. 2 is that the sealing member 82 is not supported by a spacer ring such as the spacer ring 62 in FIG. 2. Instead, the sealing member 82 is engaged with the sealing teeth 84 and 86 of the valve body 88 on the undersurface and engaged with sealing teeth 90 and 92 on the upper surface. Sealing teeth 90 and 92 are part of a cap (not shown) which encloses the entire valve to form a gas tight seal. Also, the solenoid slug 94 does not have an annular shoulder thereon such as the shoulder 58 in the valve of FIG. 2. However, the solenoid slug 94 could be formed with the same configuration as the solenoid slug 54 in FIG. 2. Other means of applying pressure in the negative y direction to the sealing member 82 may also be used. Note also that the valve body has a gas passageway 96 formed therein to conduct gas from an external port 98 coupled to an external gas reservoir (not shown) to the internal chamber 100. Note that the sealing member 82 is physically engaged by the sealing teeth 84, 86, 90 and 92 and therefore is fixed in position relative to the valve seat 96. Therefore, if the solenoid slug 94 wobbles, rotates or otherwise moves during its movements along the y axis, the sealing member 82 does not move relative to the x axis during the process of engaging the valve seat 96. Thus, the advantages of the embodiment of FIG. 2 over that of FIG. 1 are also achieved in the embodiment shown in FIG. 3. The resealing time of the embodiment of FIG. 3 is comparable to the embodiment of FIG. 2.

In both the embodiments of FIGS. 2 and 3, the distance A between the underside of the sealing members and the valve seat is approximately 10 to 15 thousandths of an inch.

Referring to FIG. 4 there is shown in cross-section another valve construction for a gas resupply valve according to the teachings of the invention. In this embodiment a valve body 110 has a flat upper surface 112 which has two ports 114 and 116 formed therein. The surface 112 may be ground flat and does not have to be optically flat. The port 114 serves as an input port for gas while the port 116 serves as an output port. A 5 mil thick foil diaphragm 118 rests on the surface 112 and is supported at sealing rings 120 and 122 which are in fact a single rubber sealing ring in the preferred embodiment. Movement of the diaphragm 118 in the x direction is restrained by retaining walls 124 and 126 in the preferred embodiment. With a circular valve construction, the retaining walls 124 and 126 are in fact a single annular retaining wall.

The port 116 serves as an inlet port to a metering volume 128. The metering volume 128 has one wall which is a diaphragm 130 in which is formed an aperture 132. This diaphragm 130 and the aperture 132 serve the same purpose as the diaphragms and apertures in the valves of FIGS. 1-3. The metering volume is in fluid communication with the laser tube through the aperture 132 and a fluid communication path 134.

A solenoid core 136 having a soft material 138 formed on the end thereof serves to open and close the valve in a manner to be described below. The soft material 138 can be CALRES™ by DuPont or any other soft material such as rubber, or soft metals such as brass or aluminum. Preferably, the materials for all elements in the valve of FIG. 4 should have a high melting point. For this reason, an all metal structure is preferred. Thus brass is the preferred material for the element 138. The reason for this preference is that during the construction of a gas laser, during the pump down stage where the laser tube is evacuated, it is desirable to heat the tube to as high a temperature as possible to speed up the process. This aids in removal of gas molecules trapped in crevasses in the surface of the metal inside the tube and in removing the monolayer of gas atoms which adhere to the walls of the metal inside the tube. The increased thermal activity of the atoms decreases the diffusion time for gas molecules coming out of crevasses and decreases the time it takes to liberate the monolayer gas atoms from the walls of the internal structure of the laser tube. Since the gas resupply valve is already attached to the laser tube during this process, it too is subjected to high temperatures. Therefore the presence of any polymers or other materials which cannot withstand the high temperatures of the bake process is undesirable.

In operation, the valve of FIG. 4 is initially sealed, thereby preventing gas flow from port 114 into the metering volume 128. This sealing occurs when the solenoid slug 136 is moved in the negative y direction thereby forcing the soft material 138 against the diaphragm 118. The force exerted upon the diaphragm causes it to come down upon and conform to the contour of the surface 112 thereby, forming a seal. This is the reason that the surface 112 should be as flat as possible although perfect flatness is not necessary. This is also the reason that the diaphragm 118 should be relatively thin. The only criterion is that the flatness of the surface 112 and the thinness of the diaphragm 118 combine to make a seal which is adequate to meet the requirement that there be a negligible leak rate when the valve is closed. In the preferred embodiment, this seal was experimentally found to be better than 1×10⁻¹⁰ liters per minute leak rate.

To recharge the laser tube when the pressure therein drops too low, the solenoid core 136 moves in the positive y direction for a short time such as 5 milliseconds. This allows the elastic diaphragm 118 to spring back to its original shape thereby creating a passageway for gas flow between the port 114 and the port 116 between the diaphragm 118 and the surface 112. This fills the metering volume 128. Since the diffusion time constant of the aperture 132 is short relative to the time that this passageway is open, no gas leaks into the laser tube during the time that the gas flow pathway between port 114 and port 116 is open. After the metering volume is filled, the solenoid core 136 again moves in the negative y direction thereby sealing the metering volume 128 from further gas input. Thereafter, the gas trapped in the metering volume 128 is drawn into the laser tube through the aperture 132 and the fluid communication path 134.

Referring to FIG. 5, there is shown a cross-section of another valve built according to the principles of the valve of FIG. 4 except the metering volume 128 and the diaphragm 130 and aperture 132 are replaced by a single output port 140. All other structures are the same and serve the same purpose. Thus the structure of FIG. 5 is a simple valve having a gas input port 142 and a gas output port 140. Of course, other materials than gas can be controlled using the valve of FIG. 5 such as liquids. If corrosive liquids are to be handled, materials must be selected for the valve structures which come into contact with the liquid which cannot be damaged by the liquid. Those skilled in the art will appreciate the selection of materials necessary to such applications.

Referring to FIG. 6, there is shown another embodiment of a valve according to the principles shown in FIGS. 4 and 5. In this valve, the principle difference is that the diaphragm 144 is permanently attached to the valve body 146 by welds 148 and 150. These welds can also be brazed connections or other forms of connection suitable for connecting the material of the diaphragm 144 to the material of the valve body. In FIG. 6, the diaphragm 144 is shown as a single line. The diaphragm 144 has bellows 150 and 152 formed therein. The purpose of these bellows is to allow for differences in the rates of thermal expansion and contraction between the diaphragm 144 and the valve body 146. Such differences could cause the diaphragm 144 to bow away from the flat surface 154 of the valve body 146 under certain conditions. In other words, the diaphragm 144 could bow up and away from the surface 154 in the positive y direction under certain circumstances. This bowing action could make it impossible to properly seal the valve between input port 156 and output port 158. The bellows 150 and 152 can expand or contract to account for these differences thereby maintaining the relative relationship in the y direction between the diaphragm 144 and the surface 154.

In the embodiment of FIG. 6, a single simple output port 158 is shown. However, those skilled in the art will appreciate that the single output port 158 may be configured as a metering volume/diaphragm/aperture/fluid communication path as shown in FIG. 4 at 128, 130, 132 and 134 respectively. Such a configuration would make the valve of FIG. 6 suitable for use in gas resupply to gas lasers having loss mechanisms.

In operation, the valve works the same way as the valves shown in FIGS. 4 and 5 in that solenoid core 160 moves in the negative y direction to force soft material 162 against the diaphragm 144 thereby causing it to contact the flat surface 154 and seal the valve. This prevents any fluid flow between the input port 156 and the output port 158. When the valve is to be opened, the solenoid core 160 is moved in the positive y direction thereby allowing the diaphragm 144 to move in the positive y direction and opening a fluid communication path between the port 156 and the port 158.

Although the invention has been described in terms of the multiple embodiments disclosed herein, those skilled in the art will appreciate many modifications which may be made to these structures to utilize the concepts disclosed herein without departing from the true spirit and scope of the invention. All such modifications, substitutions and other equivalents to structures are intended to be included within the scope of the claims appended hereto. 

What is claimed is:
 1. A gas resupply valve for a gas laser tube comprising:a valve means having a gas input for receiving gas from a resupply gas reservoir and a gas output for opening for a predetermined time interval to allow gas to flow from said gas input to said gas output; a metering volume coupled to said gas output to receive gas when said valve means is open and having one wall which is substantially nonpermeable to said gas and through which is formed an aperture having a diameter, with said diameter determining a diffusion time constant for gas moving through said aperture, with said diffusion time constant being less than said predetermined time interval; and means for coupling gas escaping through said aperture into said gas laser tube.
 2. The apparatus of claim 1 wherein said aperture has a diameter of from 10 to 15 microns.
 3. The apparatus of claim 2 wherein said valve means comprises:a valve seat formed from the walls of said metering volume and having a projecting ridge around the circumference of said metering volume; solenoid means having a winding and having a core for movement in response to electrical signals applied to said core, said core having a sealing material attached to an end of said core adjacent to said valve seat, said solenoid means for moving said sealing material into and out of sealing engagement with said valve seat under the influence of electrical signals applied to said winding.
 4. A gas resupply valve for a gas laser tube comprising:a valve body comprising a solid block of material in which cavities and passages may be formed for forming valve; a metering volume formed in said valve body having an opening for gas input and having at least one wall which is a diaphragm and which has an aperture formed wherein and having a valve seat formed integrally around the circumference of said opening into said metering volume; a fluid communication path formed in said body so as to be in fluid communication with fluid in said metering volume by way of said aperture by which path gas in said metering volume may exit said apparatus after leaking out of said metering volume through said aperture; a sealed chamber in said valve body surrounding said valve seat for storing gas inside said valve body; sealing means including a sealing member for removing said sealing member from sealing engagement with said valve seat for a predetermined time in response to a control signal to allow gas in said sealed chamber to enter said metering volume; and wherein said aperture is sized to have a diffusion time constant which is less than the time said sealing member is not in sealing engagement with said valve seat.
 5. The apparatus of claim 4 further comprising a gas resupply reservoir formed in said valve body and a fluid communication path between said resupply reservoir and said sealed chamber.
 6. The apparatus of claim 5 wherein said sealing means is a solenoid having a core and having a sealing member of material attached to the end of said core.
 7. A gas resupply valve for a gas laser tube comprising:a sealed chamber for storing gas; valve means for controlling fluid flow and having a cycle time for movement from closed to open and back to closed; and a metering volume having an opening into said sealed chamber controlled by said valve, and having one wall comprised of a diaphragm having an aperture formed therein sized to have a diffusion constant which is shorter than said cycle time of said valve.
 8. An apparatus as defined in claim 7 further comprising a valve seat formed around said opening of said metering volume, and wherein said valve is comprised of a solenoid having a coil which acts upon a ferromagnetic core by electromagnetism, said core having attached thereto a resilient sealing member which is pressed by said core into sealing engagement with said valve seat when said valve is closed.
 9. The valve of claim 8 further comprising a fluid passageway in fluid communication with said aperture for guiding fluid escaping from said metering volume to an output port.
 10. The valve of claim 9 further comprising a valve body in which said sealed chamber and said metering volume are formed, said valve seat being formed from the walls that define the opening of said metering volume, said valve seat having pointed edges which deform said resilient sealing member when said valve is in the closed position to form the seal.
 11. The apparatus of claim 10 further comprising a resupply gas reservoir formed in said body and in fluid communication with said sealed chamber.
 12. A method of recharging a gas laser having an internal cavity with gas having a gas pressure disposed therein, wherein the gas pressure can be monitored using a valve having the construction defined in claim 9 and having said fluid passageway coupled to the internal cavity of said laser comprising the steps of:filling said sealed chamber with the type of gas that exists in the internal cavity of said laser at a higher pressure than exists in said laser cavity; monitoring the gas pressure to determine when the gas pressure in said laser cavity is too low; when the gas pressure in said laser cavity is too low, opening said valve for as short an interval as possible which is long enough for said metering volume to completely fill and then closing said valve; allowing said gas in said metering volume to leak through said aperture and be guided into said laser cavity; monitoring the gas pressure to determine if the gas pressure in said laser has risen to the desired pressure; and repeating all the above steps a sufficient number of times to raise the gas pressure in said laser to the desired level.
 13. The method of claim 12 wherein the step of monitoring the gas pressure includes the step of monitoring the voltage across the electrodes in said laser.
 14. The method of claim 12 wherein the step of opening said valve includes the step of opening said valve for an interval in the range from 1-15 milliseconds. 